diff --git a/lib/ajax/service-nologin.php b/lib/ajax/service-nologin.php
index 7120adec7f2..e8f82947f93 100644
--- a/lib/ajax/service-nologin.php
+++ b/lib/ajax/service-nologin.php
@@ -28,4 +28,6 @@
  */
 
 define('NO_MOODLE_COOKIES', true);
+define('ALLOW_GET_PARAMETERS', true);
+
 require_once('service.php');
diff --git a/lib/ajax/service.php b/lib/ajax/service.php
index caaf86c66f9..3bcb8e9621e 100644
--- a/lib/ajax/service.php
+++ b/lib/ajax/service.php
@@ -38,9 +38,24 @@ require_once($CFG->libdir . '/externallib.php');
 
 define('PREFERRED_RENDERER_TARGET', RENDERER_TARGET_GENERAL);
 
-$rawjson = file_get_contents('php://input');
+$arguments = '';
+$cacherequest = false;
+if (defined('ALLOW_GET_PARAMETERS')) {
+    $arguments = optional_param('args', '', PARAM_RAW);
+    $cachekey = optional_param('cachekey', '', PARAM_INT);
+    if ($cachekey && $cachekey > 0 && $cachekey <= time()) {
+        $cacherequest = true;
+    }
+}
+
+// Either we are not allowing GET parameters or we didn't use GET because
+// we did not pass a cache key or the URL was too long.
+if (empty($arguments)) {
+    $arguments = file_get_contents('php://input');
+}
+
+$requests = json_decode($arguments, true);
 
-$requests = json_decode($rawjson, true);
 if ($requests === null) {
     $lasterror = json_last_error_msg();
     throw new coding_exception('Invalid json in request: ' . $lasterror);
@@ -54,6 +69,7 @@ $settings->set_fileurl(true);
 $settings->set_filter(true);
 $settings->set_raw(false);
 
+$haserror = false;
 foreach ($requests as $request) {
     $response = array();
     $methodname = clean_param($request['methodname'], PARAM_ALPHANUMEXT);
@@ -64,7 +80,19 @@ foreach ($requests as $request) {
     $responses[$index] = $response;
     if ($response['error']) {
         // Do not process the remaining requests.
+        $haserror = true;
         break;
     }
 }
+
+if ($cacherequest && !$haserror) {
+    // 90 days only - based on Moodle point release cadence being every 3 months.
+    $lifetime = 60 * 60 * 24 * 90;
+
+    header('Expires: '. gmdate('D, d M Y H:i:s', time() + $lifetime) .' GMT');
+    header('Pragma: ');
+    header('Cache-Control: public, max-age=' . $lifetime . ', immutable');
+    header('Accept-Ranges: none');
+}
+
 echo json_encode($responses);
diff --git a/lib/amd/build/ajax.min.js b/lib/amd/build/ajax.min.js
index 2877ff78ac8..e8ad0a854b2 100644
--- a/lib/amd/build/ajax.min.js
+++ b/lib/amd/build/ajax.min.js
@@ -1 +1 @@
-define(["jquery","core/config","core/log","core/url"],function(a,b,c,d){var e=!1,f=function(a){var b,c,e,f=this,g=null,h=0;if(a.error)for(;h<f.length;h++)b=f[h],b.deferred.reject(a);else{for(h=0;h<f.length;h++){if(b=f[h],c=a[h],"undefined"==typeof c){g=new Error("missing response");break}if(c.error!==!1){g=c.exception,e=f[h].nosessionupdate;break}b.deferred.resolve(c.data)}null!==g&&("servicerequireslogin"!==g.errorcode||e?f.forEach(function(a){a.deferred.reject(g)}):window.location=d.relativeUrl("/login/index.php"))}},g=function(a,b,d){var f=this,g=0;for(g=0;g<f.length;g++){var h=f[g];e?(c.error("Page unloaded."),c.error(d)):h.deferred.reject(d)}};return{call:function(c,d,h,i,j){a(window).bind("beforeunload",function(){e=!0});var k,l=[],m=[],n=[],o="";for("undefined"==typeof h&&(h=!0),"undefined"==typeof d&&(d=!0),"undefined"==typeof j&&(j=0),"undefined"==typeof i&&(i=!1),k=0;k<c.length;k++){var p=c[k];l.push({index:k,methodname:p.methodname,args:p.args}),p.nosessionupdate=i,p.deferred=a.Deferred(),m.push(p.deferred.promise()),"undefined"!=typeof p.done&&p.deferred.done(p.done),"undefined"!=typeof p.fail&&p.deferred.fail(p.fail),p.index=k,n.push(p.methodname)}o=n.length<=5?n.sort().join():n.length+"-method-calls",l=JSON.stringify(l);var q={type:"POST",data:l,context:c,dataType:"json",processData:!1,async:d,contentType:"application/json",timeout:j},r="service.php",s=b.wwwroot+"/lib/ajax/";return h?s+=r+"?sesskey="+b.sesskey+"&info="+o:(r="service-nologin.php",s+=r+"?info="+o),i&&(s+="&nosessionupdate=true"),d?a.ajax(s,q).done(f).fail(g):(q.success=f,q.error=g,a.ajax(s,q)),m}}});
\ No newline at end of file
+define(["jquery","core/config","core/log","core/url"],function(a,b,c,d){var e=!1,f=function(a){var b,c,e,f=this,g=null,h=0;if(a.error)for(;h<f.length;h++)b=f[h],b.deferred.reject(a);else{for(h=0;h<f.length;h++){if(b=f[h],c=a[h],"undefined"==typeof c){g=new Error("missing response");break}if(c.error!==!1){g=c.exception,e=f[h].nosessionupdate;break}b.deferred.resolve(c.data)}null!==g&&("servicerequireslogin"!==g.errorcode||e?f.forEach(function(a){a.deferred.reject(g)}):window.location=d.relativeUrl("/login/index.php"))}},g=function(a,b,d){var f=this,g=0;for(g=0;g<f.length;g++){var h=f[g];e?(c.error("Page unloaded."),c.error(d)):h.deferred.reject(d)}};return{call:function(c,d,h,i,j,k){a(window).bind("beforeunload",function(){e=!0});var l,m=[],n=[],o=[],p="",q=2e3;for("undefined"==typeof h&&(h=!0),"undefined"==typeof d&&(d=!0),"undefined"==typeof j&&(j=0),"undefined"==typeof k?k=null:(k=parseInt(k),k<=0?k=null:k||(k=null)),"undefined"==typeof i&&(i=!1),l=0;l<c.length;l++){var r=c[l];m.push({index:l,methodname:r.methodname,args:r.args}),r.nosessionupdate=i,r.deferred=a.Deferred(),n.push(r.deferred.promise()),"undefined"!=typeof r.done&&r.deferred.done(r.done),"undefined"!=typeof r.fail&&r.deferred.fail(r.fail),r.index=l,o.push(r.methodname)}p=o.length<=5?o.sort().join():o.length+"-method-calls",m=JSON.stringify(m);var s={type:"POST",context:c,dataType:"json",processData:!1,async:d,contentType:"application/json",timeout:j},t="service.php",u=b.wwwroot+"/lib/ajax/";if(h?u+=t+"?sesskey="+b.sesskey+"&info="+p:(t="service-nologin.php",u+=t+"?info="+p,k&&(u+="&cachekey="+k,s.type="GET")),i&&(u+="&nosessionupdate=true"),"POST"===s.type)s.data=m;else{var v=u+"&args="+encodeURIComponent(m);v.length>q?(s.type="POST",s.data=m):u=v}return d?a.ajax(u,s).done(f).fail(g):(s.success=f,s.error=g,a.ajax(u,s)),n}}});
\ No newline at end of file
diff --git a/lib/amd/src/ajax.js b/lib/amd/src/ajax.js
index ea1669a95e1..389680f49ff 100644
--- a/lib/amd/src/ajax.js
+++ b/lib/amd/src/ajax.js
@@ -137,9 +137,13 @@ define(['jquery', 'core/config', 'core/log', 'core/url'], function($, config, Lo
          * @param {Boolean} nosessionupdate Optional, defaults to false.
          *                  If true, the timemodified for the session will not be updated.
          * @param {Integer} timeout number of milliseconds to wait for a response. Defaults to no limit.
+         * @param {Integer} cachekey This is used in order to identify the request. If this id changes then we
+         *                  will be sending a different URL and any caching (eg. browser, proxy) knows that it
+         *                  should perform another request and not use the cache. Note - this variable is only
+         *                  used when we are calling 'service-nologin.php'. See MDL-65794.
          * @return {Promise[]} Array of promises that will be resolved when the ajax call returns.
          */
-        call: function(requests, async, loginrequired, nosessionupdate, timeout) {
+        call: function(requests, async, loginrequired, nosessionupdate, timeout, cachekey) {
             $(window).bind('beforeunload', function() {
                 unloading = true;
             });
@@ -149,6 +153,8 @@ define(['jquery', 'core/config', 'core/log', 'core/url'], function($, config, Lo
                 methodInfo = [],
                 requestInfo = '';
 
+            var maxUrlLength = 2000;
+
             if (typeof loginrequired === "undefined") {
                 loginrequired = true;
             }
@@ -158,6 +164,16 @@ define(['jquery', 'core/config', 'core/log', 'core/url'], function($, config, Lo
             if (typeof timeout === 'undefined') {
                 timeout = 0;
             }
+            if (typeof cachekey === 'undefined') {
+                cachekey = null;
+            } else {
+                cachekey = parseInt(cachekey);
+                if (cachekey <= 0) {
+                    cachekey = null;
+                } else if (!cachekey) {
+                    cachekey = null;
+                }
+            }
 
             if (typeof nosessionupdate === "undefined") {
                 nosessionupdate = false;
@@ -193,7 +209,6 @@ define(['jquery', 'core/config', 'core/log', 'core/url'], function($, config, Lo
             ajaxRequestData = JSON.stringify(ajaxRequestData);
             var settings = {
                 type: 'POST',
-                data: ajaxRequestData,
                 context: requests,
                 dataType: 'json',
                 processData: false,
@@ -207,6 +222,10 @@ define(['jquery', 'core/config', 'core/log', 'core/url'], function($, config, Lo
             if (!loginrequired) {
                 script = 'service-nologin.php';
                 url += script + '?info=' + requestInfo;
+                if (cachekey) {
+                    url += '&cachekey=' + cachekey;
+                    settings.type = 'GET';
+                }
             } else {
                 url += script + '?sesskey=' + config.sesskey + '&info=' + requestInfo;
             }
@@ -215,6 +234,19 @@ define(['jquery', 'core/config', 'core/log', 'core/url'], function($, config, Lo
                 url += '&nosessionupdate=true';
             }
 
+            if (settings.type === 'POST') {
+                settings.data = ajaxRequestData;
+            } else {
+                var urlUseGet = url + '&args=' + encodeURIComponent(ajaxRequestData);
+
+                if (urlUseGet.length > maxUrlLength) {
+                    settings.type = 'POST';
+                    settings.data = ajaxRequestData;
+                } else {
+                    url = urlUseGet;
+                }
+            }
+
             // Jquery deprecated done and fail with async=false so we need to do this 2 ways.
             if (async) {
                 $.ajax(url, settings)
diff --git a/webservice/upgrade.txt b/webservice/upgrade.txt
index d5b959d5c5a..407c12a1f23 100644
--- a/webservice/upgrade.txt
+++ b/webservice/upgrade.txt
@@ -3,6 +3,13 @@ information provided here is intended especially for developers.
 
 This information is intended for authors of webservices, not people writing webservice clients.
 
+=== 3.8 ===
+
+* Ajax calls can now specify a cache key. This allows for better caching capabilities on servers. If a cache key
+  is passed and the web service call does not require the user to be logged in we will attempt to use GET for the
+  request. This allows for things like proxy caching on URLs. The cache key must be changed if we do not want to
+  retrieve what has been cached and want to perform the request again.
+
 === 3.7 ===
 
 * External function core_webservice_external::get_site_info() now returns the current site theme (for the user).